A lithium-ion secondary battery is widely used as a power source for, e.g., notebook computers, video cameras, cellular phones, and electric cars. As such a lithium-ion secondary battery, a lithium-ion secondary battery having a structure in which the circumference of the battery body is surrounded by a case is used. As such a battery case material, it is publicly known that a battery case material has a structure in which, for example, an outer layer made of a stretched polyamide film, an aluminum foil layer, an inner layer made of unstretched polypropylene film are integrally bonded in this order (see Patent Document 1).
Such battery case material is formed into various battery shapes, and therefore, is required to have high deep-drawing formability. To give it high deep-drawing formability, conventionally, for example, fatty acid amide series lubrication giving component is coated onto a surface of an outer layer film to enhance the sliding performance of the battery case material into the die at the time of the molding (see Patent Document 2), or the outer layer film is increased in thickness with respect to the thickness of the aluminum foil layer.
Patent Document 1: Japanese Unexamined Laid-open Patent Publication No. 2001-6631
Patent Document 2: Japanese Unexamined Laid-open Patent Publication No. 2002-216714